Neo4j

Neo4j is a more specialized product than most databases on this list. It describes itself as an "embedded, disk-based, fully transactional Java persistence engine that stores data structured in graphs rather than in tables." For this reason, it's suited to storing data items that have complex relationships (for example, road maps, social network relationships, etc.) rather than the traditional key-value stores or JSON documents. Neo4j provides full ACID conformity.

Due to its unique design, the database has multiple forms of querying, including a pattern matching query language (Cypher) and a graph-traversal language (Gremlin). Neo4j uses Groovy for scripting.

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